Several aspects of steroid biochemistry as it is related to hormonally dependent breast tumors are to be studied. We intend to determine whether estrogen dependent breast tumors can be identified by the detection of a specific product similar to the "estrogen induced protein "formed in the uterus in response to estrogen stimulation. This protein, induced in the breast will be detected by a double isotope procedure, but the major thrust will be to develop a radioimmunoassay for clinical evaluation. In addition the steroidogenic capacity of malignant breast tissue as well as surrounding tissue and fat will be studied and the hormonal factors, if any, controlling this synthesis will be determined. The products of the following steroidogenic enzymes will be unequivocally identified: 1) cholesterol side-chain cleavage enzyme, 2) 17 alpha-hydroxylase and C-17,20 desmolase, 3) C19-aromatase. These experiments will be correlated with both the content of estrogen receptor and endogenous estrogen in the tissue. The determination of the tissue estrogen will be performed by gas chromatography/mass spectrometry. In order to facilitate and increase the sensitivity of the assay of estrogen receptors in breast cancer: 1) estradiol labeled in the D ring at C-16 with radioiodine is being synthesized, 2) an immunohistochemical procedure for the detection of this binding protein is being developed. Finally, experiments will be performed to identify the "immunoreactive" estrogen found in the plasma of immature rats and to determine whether this adrenal product is responsible for the increased sensitivity of the young rodent to the induction of breast tumors by chemical carcinogens. This compound presumably a steroid is found in large quantities in the immature animal and is the only "hormone" known to appear prior to the appearance of the increased responsiveness of the breast to carcinogenics.